I want some suggestions, with best combination of security programs [antivrius, antispyware and others that exists ] because I don't know what to use, and I am formatting my PC a lot of times per month. So, I want a very good suggestion.

Thanks!

This is the combination i use :

McAfee Antivirus Professional,
ZoneAlarm Firewall,
SpyBot - Search and Destroy

Can run smoothly, all three of them,
if you have enough computer resources.

1.50 gb RAM 80gb space, 128mb video and that's all, what do you think, they will work good?

Yep. Anything above 1GB RAM will run those 3 apps fine!

ok thanks for that suggestion I'll try it !

Most of good Anti-virus/spyware programs these days come up with their built-in Firewall as well so you should be careful when deciding what to install. If more than one security program with the same feature (Such as two Firewalls) run on your computer, they can cause major problems. The best solution I suggest is that you install only one Internet Security Suite program so you will fully be protected and don't need to care about your software fighting with each other.

If you need help choosing good security softwares, take a look at Top Ten Reviews' Software Section, they have side-by-side comparison chart so you can decide which one to use
I personally recommend ZoneAlarm Security Suite as it doesn't take much resources.

Good luck finding your favorite software

Avast anti virus + spybot search and destroy + some Win Vista's inbuilt security

I would decide for a combination of AV, firewall and anti-vandalism software from one vendor, regardless McAfee, Norton or whatever. Such security suites are designed to interact with each other and easy to manage.

If you run a LAN and security is one of your biggest concern, you also should decide to centralize this by buying a dedicated security appliance that filters viruses and spam mails and also acts as a firewall directly before anything harmful reaches your internal network. Anyway, this is a question of your available budget ;-)